1. Field of the Invention
This invention relates generally to protection systems for computer hard disk drives in portable computers and, more particularly, to a reflexive system for unloading the heads of a hard disk drive in the event the computer is dropped or jolted.
2. Description of Related Art
Portable personal computers (PCS) have become increasingly popular. Part of this popularity is due to providing portable computers with much the same power and features of desk top workstations. Among these features are hard disk drives which are now common in portable computers.
Portable computers are subject to forms of failure which are generally not a problem for desk top workstations. They can run out of power during battery operation and they can be dropped. While this latter jeopardy is a threat to every component in the system, it is the hard disk drive which has the lowest threshold of failure in the event the computer is dropped. A typical hard disk drive includes at least one rotatable magnetic disk which is supported on a spindle and rotated by a disk drive motor. The magnetic recording media on each disk is in the form of an annular pattern of concentric data tracks (not shown) on disk.
At least one slider is positioned on the disk, each slider supporting one or more magnetic read/write heads. As the disks rotate, the slider is moved radially in and out over disk surface so that heads may access different portions of the disk where desired data is recorded. Each slider is attached to a positioner arm by a suspension. The suspension provides a slight spring force which biases the slider against the disk surface. Each positioner arm is attached to an actuator assembly. The actuator assembly often includes voice coil motor (VCM). The VCM comprises a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the current signals supplied by the actuator controller.
During operation of the disk drive system, the rotation of the disk generates an air bearing between the slider and the disk surface which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of the suspension and supports the slider off and slightly above the disk surface by a small, substantially constant spacing during normal operation.
The various components of the disk drive system are controlled in operation by control signals generated by a control unit. Control signals include, for example, control signals and internal clock signals. Typically, the control unit comprises logic control circuits, storage means and a microprocessor. The control unit generates control signals to control various system operations such as drive motor control signals and head position and seek control signals. The control signals provide the desired current profiles to optimally move and position the slider to the desired data track on the disk. Read and write signals are communicated to and from the read/write heads by means of a recording channel.
The hard disk drive is so vulnerable to shock because it is dependent on the maintenance of a very small gap between the drive heads and the surface of the hard disks. The size of this gap is a key factor in the quantity of data which can be stored on the disk. In general, the smaller the gap, the more data can be stored. Thus, small, and hence vulnerable, gap dimensions are the rule for hard disk drives. The technology routinely used to obtain small gap spacing is aerodynamic. The head is literally flown over the disk surface to place the head as close to the disk surface as possible without allowing contact. If the head were to contact the disk, the result could be both the destruction of the head and the removal of magnetic material (and hence data) from the disk surface.
Disk drive manufacturers recognize this hazard and attempt to address it by shock mounting their drives, by publishing the operating G-force limits their drives can tolerate, by providing a position where the heads may be "parked" which is not over data on the disk surface, and by providing an unload mechanism to lift the heads away from the disk surface so that the drive can tolerate accelerations which are far greater than are tolerable when the heads are "loaded" in the normal operating position.
The prior art describes the use of accelerometers for shock detection and to initiate strategies designed to limit the damage to the data in the event of an impact. U.S. Pat. No. 4,862,298 issued to Genheimer et al., describes an impact detection method used to generate a write-fault signal to the computing system. This signal is used to prevent data destruction by off-track writes and to cause head retraction in the event of severe impacts.
U.S. Pat. No. Re. 35,269 issued to Comerford describes a protective reflex system for a portable computer in which an accelerometer monitored by a dedicated processor detects accelerations corresponding to a falling condition and parks the heads away from data prior to impact occurring.
The problem with these techniques is that in the first case remedial action is taken after the shock event and may be too late to prevent damage to the heads and to the magnetic coating on the disk surface, and in the second case, a suitable accelerometer and dedicated processor are required adding to the system complexity and cost.
It is apparent that there is a need for a shock protection device for a hard disk drive that prevents damage to the heads and disk surfaces in the event of a fall without adding to the cost and complexity of the system.